Perpendicular recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole layer with a small surface area at an ABS, and coils that conduct a current and generate a magnetic flux in the main pole that exits through a write pole tip and enters a magnetic media (disk) adjacent to the ABS. The flux is used to write a selected number of bits in the magnetic media and typically returns through a shield structure to a back gap region that connects the main pole with the return shield. In some cases, the return shield may also serve as the top shield in a read head that is formed below the write head in a combined read-write structure. A PMR head which combines the features of a single pole writer and a double layered media (magnetic disk) has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density.
Perpendicular magnetic recording has become the mainstream technology for disk drive applications beyond 150 Gbit/in2. As the demand for slim drives based on PMR head technology has increased, stray field robustness (SFR) or external field robustness (EFR) becomes more and more important when considering the use of an aluminum cover/base to reduce both thickness and weight for the device. Besides the traditional EFR issue, the edge of the writer or reader shield near the ABS may cause erasure when an external field is applied. The SFR issue is associated with poor writing, asymmetry writing, and/or pole erasure (PE) that can cause on-track bit error rate (BER) loss and servo erasure when a stray field is applied.
Besides, with the growing demand for cloud storage and cloud-based network computing, high and ultra high data rate recording becomes important for high-end disk drive applications. It is essential to design a PMR writer that can achieve optimum high data rate performance without sacrificing thermo-mechanical (T/M), adjacent track and wide area erasure (ATE/WATE), and stray field or external field robustness (SFR/EFR) requirements.
For high data rate performance, a compact writer with smaller dimensions in both yoke length and ABS width is a preferred direction. However, small writer protrusion profile associated with a small/compact writer is not favored from a T/M point of view due to delayed writer touch down (TD) detection. This result may cause writer wearing and related reliability issues. Furthermore, when the ABS width of a writer is reduced, EFR at the edge of the reader shield may become worse as external field overloads towards the wider reader shield side unless the reader shield shrinks accordingly. Thus, greater flexibility in the write shield structure and better control of stray field effects are needed to accommodate a smaller write pole width while improving EFR and SFR to a level that is characteristic of wider ABS width writers.
Reducing the magnetic spacing from read/write heads to the magnetic media during both writing and reading is another important factor in achieving better performance in high density recording. The writer and reader are separated by several microns in a typical recording head and are made of several different materials each having a unique coefficient of thermal expansion (CTE). Therefore, the protrusion of the reader and writer are usually quite different due to the effect of varying operating temperatures, applying dynamic flying height (DFH) power to actuate the reader or writer, or from write current excitation. In addition, the point with minimum spacing to disk could be located away from either the reader or the writer, imposing further restrictions to achievable magnetic spacing during reading and writing. Improvements in PMR head design are needed to control the protrusion differences at the writer, the reader and the minimum point, and its variation. In particular, for the touchdown and then back off mode of operation using DFH, writer protrusion should be as close as possible to the reader protrusion to improve touch down detection.